1. Field of the Invention
The present invention relates to a super-charged turbo-compound hybrid engine apparatus and a control method of such apparatus, in particular for industrial vehicles. The invention finds application also in the field of marine engines, transport vehicles and agricultural applications, independently from the kind of feel, gasoline, diesel, gas or hydrogen.
2. State of the Art
Two-stage turbocharging has been proposed as a means of achieving high efficiency in engines, in particular heavy duty diesel engines, such as those for industrial vehicles or ships. Two turbosuperchargers are placed in series on the engine intake line, driven by turbines placed on the exhaust line, which can also be placed in series, or arranged in another way.
The turbocompound solution comprises two turbines placed in series on the exhaust line, where the low pressure one is connected to the crankshaft of the diesel engine by means of a step down gear. Therefore, such second turbine provides a supplementary torque to the engine.
A double turbocompound scheme is disclosed by the patent EP2042705. It shows a high pressure turbine and a low pressure turbine arranged on the exhaust line. Such turbines may be placed in parallel or in series between each other by means of appropriate connections and reduction valves, especially when the two turbines are parallel configured, due to the different characteristics of the two turbines.
The high pressure turbine is mechanically connected with a high pressure supercharger.
The low pressure turbine is connected to the crankshaft by means of a mechanical link. The link comprises means to reduce the speed variations, placed between the second turbine and crankshaft, as in the case of conventional turbocompound engines. Moreover, such mechanical link also connects a low pressure supercharger, arranged on the intake line, upstream with respect a high pressure supercharger, the latter being directly connected to the intake of the combustion engine.
Driven Compressor and Powerturbine are coupled via hydrodynamic clutch and redaction gear to the engine. The job of the hydrodynamic clutch is to reduce the torque oscillation from crankshaft to the Turbomachinery gears. An additional function of the clutch in EP2042705 is to connect and disconnect the driven Compressor and Powerturbine from the engine. This function enable to run the system as a free running low pressure turbocharger with some additional gear friction losses.
WO 2010/066452 teaches to manage the slip of the hydrodynamic clutch boost, for controlling backpressure, of exhaust gases, and EGR.
The low pressure supercharger receives mechanical energy from the engine or also from the low pressure turbine via such link.
DE 102005003714 shows a two stage compound system. Thanks to this scheme, the driven low pressure compressor needs high energy to generate boost. However, the controllability of the mechanical driven low pressure compressor is hard to handle.
A classic turbocompound scheme is able to provide a fuel consumption reduction, ranged between the 5 and 10%, and a better power density ranged between the 100 and 110%, with respect to a combustion engine provided with variable turbine geometry (VTG).
Power density is defined as Power [kW]/engine displacement [l (liter)] so called specific power output. This output is between 30-34 kW/l for modern heavy duty diesel systems with electronic controllable VTG. Two stage and two stage compound systems can reach 50 kW/l.
At the opposite, a classic two stage turbocharged scheme is able to provide a lower fuel consumption reduction, ranged between the 0% and 5% and a better power density ranged between the 115 and 130% with respect to a VTG scheme. The term turbocharger is synonymous with supercharger or compressor.
It's also known, a so called, “electric turbo-compound scheme” comprising a high pressure supercharger axially connected with a high pressure turbine and a low pressure turbine axially connected with an electric generator which produces electric energy. An electric motor is also connected with the crankshaft of the combustion engine. A first inverter converts the energy produced by the electric generator in direct current injected in a DC bus and a second inverter, connected with said DC bus, is suitable to power supply the electric motor. The latter supplies a supplementary torque to the combustion engine.
With respect to the mechanical turbo-compound scheme. In the electric scheme the low pressure turbine is therefore disconnected from the engine crankshaft and that means it is not affected by the engine oscillations. At the same time also the transmission of the supplementary torque to the crankshaft of the combustion engine can be performed in an independent way by means of the electric motor connected to the crankshaft.
Although such undoubted advantages with respect to the mechanical schemes, anyway also known electric turbo-compound schemes does not allow to overcome appreciably some drawbacks such as the low power density and the high fuel consumption. Moreover the known electrical schemes and the known mechanical schemes do not allow an appreciable recuperation strategy as well as an markedly transient performance.